1. Field of the Invention
This invention relates to hydrocarbylthionophosphine sulfide dimers and their preparation. In particular the invention is directed to the preparation of a disulfide dimer of ethylthiophosphonic disulfide (EPTD).
2. Related Art
It is known in the art to prepare hydrocarbylthiophosphine sulfide by the reaction of hydrogen sulfide with a hydrocarbylthiophosphonic dichloride. The known prior art methods are exemplified in "Topics in Phosphorus Chemistry", Vol. 2, pp. 50-59 (John Wiley & Son 1980) wherein a process for producing thionophosphine sulfides is disclosed comprising the reaction of an alkyl or aryl phosphonothioate dichloride with hydrogen sulfide at elevated temperatures. It is indicated that the temperature at which the reaction occurs is dependent upon the phosphonothioate dichloride used and is usually above 160.degree. C. It is further indicated that the reaction rate is slow and requires several hours for completion but that the rate of reaction increases in the presence of a tertiary amine. Further it is stated that in such instances, where a tertiary amine is used, the reaction is usually carried in an inert solvent such as a hydrocarbon, methylene chloride or ether at temperatures ranging from 40.degree.-150.degree. C. which is below the melting point of the product.
In U.S. Pat. Nos. 3,155,708 and 3,155,709 there is disclosed a process for preparing hydrocarbylphosphonic phosphonodithioic acid and esters thereof. The method disclosed for making the intermediate hydrocarbyl thionophosphine sulfide in each instance was by reacting a hydrogen sulfide with hydrocarbylthionophosphonic dichloride. In the examples provided it is disclosed that the hydrocarbylthionophosphine sulfide product when formed is a solid which is recovered by being broken out of the reaction vessel.